NPR has obtained a report from the Inspector General of the Labor Department that describes an incident last year in which the nation's coal mine safety chief and agency lawyers withdrew a legitimate safety citation and order "not based upon the merits" but "to avoid the appearance of retaliation and possible Congressional scrutiny."

The report says that Kevin Stricklin, the Administrator of Coal Mine Safety and Health at MSHA, "expressed some regret about ever having agreed to vacate the citation and order, because he believes that they were based upon legitimate safety concerns..."

The safety violation involved a contentious relationship between Massey Energy, the owner of the Upper Big Branch mine at the time, MSHA investigators and representatives of the United Mineworkers of America (UMWA), who worked side by side conducting their own investigations of the tragedy.

A Massey Energy consultant was deemed unqualified to work underground without more mine safety training and was cited for failing to "adequately recognize and avoid hazards in the mine" and for not being "responsive to warnings and requests" about safety, according to the Inspector General report.

The Massey consultant was also ordered out of the mine until he received adequate training.

The incident was one of several cited in the report, which resulted from Massey Energy complaints about "retaliation and intimidation" aimed at the company's consultants by chief MSHA investigator Norman Page.

Page was removed from the investigative team for several months last year while the complaints were investigated.

The Inspector General's report says "our inquiry did not substantiate the allegations that Mr. Page engaged in a campaign or pattern of intentional intimidation or retaliation" but it also said Page made statements "that could have been perceived and/or interpreted as intimidating."

Those statements were made in a private meeting with a Massey Energy consultant who later accused Page of threatening to flood the consultant and his company with safety citations and orders. Page denied the accusation.

The report was actually produced in November and was kept under wraps until this week after NPR filed a Freedom of Information Act request.

The citation dismissal involving Stricklin and un-named attorneys from the Solicitor's Office of the Labor Department drew a strong reaction from the leading Republican and Democrat on the House Education and Workforce Committee.

"Congressional scrutiny should never be used to compromise health and safety," says George Miller (D-CA), the ranking Democrat on the committee, "nor should it ever be used as a bargaining chip to undermine enforcement of the law."

Committee Chairman John Kline (R-MN) intends to question the Department of Labor on this issue.

"I am deeply concerned the department would vacate a citation for any reason other than the merits of the law," Kline tells NPR. "Brushing aside a safety violation out of fear about congressional scrutiny is simply unacceptable."

Kline was also disturbed about findings in the report that indicate Massey Energy and UMWA representatives prompted the intimidation and retaliation allegations.

"The idea that outside interests could interfere with the work of the investigation team is deeply troubling," Kline says. "This Inspector General report deserves further scrutiny to help determine whether current policies governing investigations are in the best interest of mine workers' safety."

The report clears Page of any wrongdoing but the behavior that triggered the allegations raises concerns about his usefulness, and, possibly, the usefulness of the conclusions of the MSHA investigation, in an ongoing federal criminal probe.

"This report and the allegations in this report create a challenge for prosecutors who would want to use MSHA's conclusions in a criminal case," according to an attorney familiar with the Upper Big Branch investigation, who spoke on the condition of anonymity.

"Even though the Inspector General found no intimidation or retaliation on the part of MSHA or lead investigator Norman Page, the appearance of bias could still be raised as an issue and its unclear how a jury would respond," the attorney added.

University of Michigan law professor David Uhlmann, who is a former Justice Department prosecutor, believes the impact on the criminal investigation will be limited.

"The investigator's approach may have been unduly aggressive at times, but that hardly is unusual," Uhlmann says. "At most, it would compromise him as a witness; it does not undermine the integrity of the investigation."

MSHA's investigative team issued a final report in December blaming the Upper Big Branch explosion on failed safety systems and a culture at Massey Energy that allegedly put production before safety.

In response, spokesman Jesse Lawder said "we're going ton decline to be interviewed. I would refer you to DOL's response to the IG report."

In that written response to the report, the Labor Department supports the cancellation of the citation involving insufficient training for the Massey Energy consultant, citing a condition and agreement to receive additional training. Deputy Secretary of Labor Seth Harris makes no mention of the report's finding that the citation was vacated "not based on the merits."

But Harris says that "Page should have foreseen the misunderstandings and misconceptions that resulted in his actions being perceived and/or interpreted as intimidating." Still, Harris says the agency plans no action in response.

Next Tuesday, MSHA plans to release its own internal review of the agency's actions and possible inactions that may have contributed to the conditions that led to the Upper Big Branch explosion.

The agreement does not keep federal prosecutors from pursuing criminal charges against former Massey Energy managers and executives.

Update at 7:25 p.m. ET. Union Reaction:

UMWA spokesman Phil Smith objects to Rep. Kline's reference to the union as an "outside interest" that "could interfere with the work of the investigation."

"The Union was not 'an outside' interest," Smith says, "but was designated by miners as their representative in the investigation. Second, the Union may have challenged [Massey Energy], but the Inspector General did not find any misconduct on the part of the UMWA representatives. And third, when it became evident that [MSHA] was willing to compromise a citation for reasons other that its own merits, UMWA representatives properly objected."